A chemical sensor for detecting a chemical substance by using light emission caused by a chemical binding is being studied. Specifically, a probe material that is specifically bound to a target material to be detected is adhered onto a sensor, and a sample containing the target material is supplied to the sensor. As a result, the target material is bound to the probe material. For example, a fluorescent label is introduced to a bound body of the target material and the probe material, and fluorescence is generated on the bound body by irradiation with excitation light. As a result, the fluorescence is detected by a photoelectric conversion element, and thus it is possible to confirm the existence of the target material in the sample.
In such a chemical sensor, if the excitation light for exciting the fluorescent label is detected by the photoelectric conversion element, the excitation light cannot be distinguished from the fluorescence which should be detected, so it is necessary to separate the excitation light from the fluorescence and remove the excitation light.
For example, Patent Document 1 discloses an organic molecule detection semiconductor element provided with an optical filter and DNA immobilization film which blocks out excitation light and causes only fluorescence to pass therethrough. The optical filter and DNA immobilization film is a multilayer film optical filter formed by laminating a silicon dioxide film, an aluminum oxide layer, a magnesium oxide film, and the like and removes ultraviolet light (excitation light) by using interference of light.    Patent Document 1: Japanese Patent Application Laid-open No. 2002-202303 (paragraph [0039], FIG. 1)